The movie begins with a young girl, Anna (Emily Browning), making out with her boyfriend Matt on the beach at a party. After he tells Anna he loves her and has "a condom", she gets up to leave. As she goes, her sister Alex (Arielle Kebbel) asks if everything is all right. On her way through the woods to her house, Anna encounters three white garbage bags. When she goes to open them, the cadaver of a redheaded girl falls out. As Anna recoils, the girl's head snaps around and speaks. Screaming and afraid, Anna runs home. She then hears a bell that her terminally ill mother rings when she needs something. Anna is concerned because her mother is not supposed to be alone. However, after she leaves the boathouse her mother is in, it explodes into flames and a piece of debris comes flying towards her, burning her. It is then revealed that this is a dream Anna is having.

The film takes place at an undetermined point in the future, when humanity has developed advanced robotic technology with enhanced artificial intelligence. By means unknown, their own machines instigate a cybernetic revolt against humanity, triggering a global civil war between the machines and the humans. As the war presses on, the machines develop an army of invincible cyborgs, completely ruthless and virtually indestructible, to try and eliminate the human race once and for all.